1. Field of the Invention
The present invention relates to a secondary battery, and more particularly, to a secondary battery that can improve the assembling workability and reliability of the battery.
2. Description of the Prior Art
Generally, secondary batteries have been actively developed along with the rapid development of lightweight and high function portable wireless devices such as video cameras, cellular phones, portable computers and others. The secondary battery includes, for example, a nickel-cadmium battery, a nickel-hydrogen battery, a nickel-zinc battery and a lithium secondary battery, etc. Among these battery chemistries, the lithium secondary battery has been widely used for advanced electronic devices because it can be recharged and is also relatively small so as to provide a high capacity battery with a high operating voltage and high energy density per unit weight.
The lithium secondary battery includes an electrode assembly constituted of cathode and anode plates and a separator in a can with electrolyte. An upper opening of the can is sealed by a cap assembly. A cap plate of the cap assembly is combined to the upper opening of the can by welding, etc.
An insulation case is inserted into the can and is provided at the upper part of the electrode assembly before the cap plate of the cap assembly is coupled to the can. The insulation case interposed between the electrode assembly and cap assembly prevents an electrical short between the electrode assembly and the cap assembly.
However, there has been a problem in the procedure in which the electrode assembly and insulation case are inserted into the can.
Usually, a seating projection is formed at the upper part of the can to seat the cap plate of the cap assembly. Accordingly, after the electrode assembly is inserted into the can past the seating projection, the insulation case is more deeply inserted into the can.
The insulation case is generally easily inserted to the position of the seating projection formed at the upper part of the can. However, when the insulation case is more deeply inserted inside the can, the insulation case typically must be forcibly inserted by a pressing force that is applied downward. Accordingly, when the insulation case is not exactly inserted to an assembling position on the upper part of the electrode assembly, the insulation case may twist or rotate such that a portion of the insulation case may project out of the can. Particularly, when a projection contacted to the inner surface of the can is formed at the side surface of the insulation case, this problem occurs more often and the assembling error rate is increased. That is the reason that contact area between the projection of the insulation case and the inner surface of the can is relatively small and thus if the pressing force is uneven, or if a unit guiding the insulation case is not provided at the inner surface of the can the insulation case may be more often separated from the can.
As described above, when the insulation case is separated from the can, the entire assembling process is delayed.
In addition, a problem may occur even when the insulation case is not separated from the can after the insulation case is forcibly inserted into the can.
In other words, the conventional insulation case is inserted inside the can in a state that the insulation case is usually placed on the electrode assembly. However, the electrode assembly is formed by winding cathode and anode plates and the separator interposed between them together. The separator is formed wider than the cathode and anode plates to insulate the two plates from each other. Accordingly, the separator is projected out of upper and lower parts of the completely assembled electrode assembly by a certain length. Accordingly, when the insulation case is inserted into the can and assembled to press against the upper part of the electrode assembly, the separator projected out of the upper part of the electrode assembly is compressed by the insulation case. Over time, the resiliency of the separator may result in the separator protruding out of the can and urging the insulator case upward.
Usually, after the insulation case is inserted into the can and the cap plate is seated on the seating projection formed at the upper part of the can, a bonding process is performed such as welding, etc. to secure the cap plate to the can. However, the reliability of the welding process is degraded when the insulation case inserted into the can is projected out of the can by the resilience of the separator. The insulation case is easily projected out of the can by resilience of the separator projected out of the upper part of the electrode assembly because the insulation case is often very shallowly inserted into the can.
As described above, the conventional insulation case is forcibly inserted into the can and thus the assembling the insulation case into the can is problematic.
In addition, welding reliability of the cap plate welded to the upper part of the can can be degraded because the insulation case is projected out of the can after the insulation case is assembled in the can by the resiliency of the separator when it is in contact with the separator.